Neuroscientists studying the process of song learning and memory in songbirds have been limited to three species that are easily kept in the lab: sparrows, zebra finches, and canaries. These species exhibit very different patterns in the timing and duration of learning and their tendency to copy whole song types. Very little is known about why these different learning strategies have evolved. This study continues our field-based program of examining the communication consequences of different song learning strategies in wild songbirds with repertoires of song types. Our working hypothesis is that males invoke different cognitive processes when singing to rival males than when singing to females. Having completed our studies of an age-restricted learner, the song sparrow, we plan to continue our studies of an intermediate learner, a tropical wren, and to begin the study of an open-ended learner with a very large repertoire and heterospecific mimicry abilities, the mockingbird. We shall take advantage of new technology, including microphone array recording and interactive playback, to quantify how males use their song repertoires and their shared and unshared songs to communicate aggressive intentions to other males and their attractiveness to females. For both species, we shall: 1) quantify the acquisition and nature (copied versus improvised) of new song types with respect to neighbors and relate their learning behavior to their age, survival, and reproductive success, 2) monitor the simultaneous singing of adjacent males as a function of their aggressive behavior, and compare observed song-type delivery patterns to various random and non-random models, 3) perform interactive playback experiments to test the salience of songs that match the bird's own song to different degrees, 4) test the "keep-out" function of shared (local) versus unshared (foreign) songs, and 5) pinpoint the ecological and demographic factors that may be selecting for different learning, copying, and singing strategies. For the mockingbird, we shall study the brain anatomy of this amazing songster and compare immediate-early gene activity in countersinging versus courtship-singing individuals. This research relates to recent work on human language learning showing that some aspects of acquisition occur and are restricted to early ages, whereas other aspects of acquisition can accommodate to the social environment experienced by adults.